Host components

Our next subject involves the factors required to design a phosphor. We must consider 1) choice of the host components, 2) choice of the activator, and 3) killers of luminescence. 

The host cation is therefore limited to those ions which have the rare gas electron configuration, or closed electron shells, and therefore are optically inactive. In the following diagram, we show those cations which can function to form a phosphor having the desired quantum efficiency  

In this diagram, the required valence state of the cations are shown in the parentheses at the top. The suitable cations are those in the following subgroups of the periodic table  

In the choice of anions for design of phosphors, we have already established that anions can be divided into two classes, those that are optically inert and those that are optically active. The optically inert anions useful in designing phosphors are shown in the following diagram  

Each represents a class of anions. That is, the orthosilicate is Si04 . But this anion is one of many silicate anions which include Si207 , SiOa  

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Hofmann- and Werner-Type Inclusion Compounds. There is a wide range of clathrates having as the host component inorganic coordination compounds represented by the general formulae M(NH2)2 (CN) and X2Y4. The first formula is typical of Hofmaim-type clathrates... 

PGSE measurements on polyethylene oxide) in aqueous dextran solutions were performed by Brown and Stilbs A2) as function of the concentrations of both polymers. The results for D(PEO) depend on the product of the concentration and the intrinsic viscosity of the dextran (host) component, and suggest that coil overlap in the concentrated host solution is the principal impediment to PEO diffusion. 

Yoshida, N. (2008). Trypanosoma cruzi infection by oral route How the interplay between parasite and host components modulates infectivity. Parasitol. Int. 57(2), 105-109. 

Supermolecules generally comprise a host component with convergent binding sites and a guest component with divergent binding sites. 

Lipkowski, J., Pawlowska, M., Sybilska, D., Experimental-study of selectivity and column efficiency in clathrate chromatography using Werner complexes as clathrate host components. 1. Relationship between selectivity of Ni(Ncs)2(4-methylpyridine)4. Guest clathrate sorbents and composition of the mobile phase. J Chromatogr. 1979,176,43-53. 

Use of chiral single crystals to convert achiral reactants to chiral products in high optical yield application to die di-Jt-methane and Norrish type II photorearrangements, J. Am. Chem. Soc., 108, 5648-5649. (b) Chen, J., Pokkuluri, P. R., Scheffer, J. R., and Trotter J. (1990) Absolute asymmetric induction differences in dual pathway photoreactions, Tetrahedron Lett., 31, 6803-6806. (c) Fu, T. Y., Liu, Z., Scheffer, J. R., and Trotter, J. (1993) Supramolecular photochemistry of crystalline host-guest assemblies absolute asymmetric photorearrangement of the host component, J. Am. Chem. Soc., 115, 12202-12203. (d) Leibovitch, M.,... 

Other closely related microheterogeneous environments such as micelles [70] or tailored electron relays capable of micellization upon reduction [71], operate by related hydrophilic-hydrophobic interactions in controlling photosensitized ET processes. Similarly, separation of photoproducts at the molecular level, by means of hydrophobic interactions, has been accomplished by utilizing cyclodextrin receptors [66, 72]. This host component selectively associates one of the photoproducts into the hydrophobic receptor cavity and consequently back ET is retarded. 

Fig. 6.2. Prominent parasite antigens and host components in Echinococcus granulosus sheep cyst fluid (SCF). Labelled fluid was immunoprecipitated with lane 1, normal rabbit serum lane 2, rabbit anti-SCF lane 3, preabsorbed rabbit anti-SCF lane 4, rabbit anti-sheep whole serum. Antigens were reduced prior to electrophoresis. The major parasite antigens are shown arrowed at Mr 38000, 20000, 16000 and 12000. D.F., diffusion front. (Reprinted with permission from Molecular and Biochemical Parasitology, 25, Shepherd, J. C. McManus, D. P., Specific and cross-reactive antigens of Echinococcus granulosus hydatid cyst fluid, 1987, Pergamon Journals Ltd.)...

Affinity Interactions at Interfaces Using Immobilized Photoisomerizable Host Components... 

RECOGNITION PHENOMENA AT SURFACES USING PHOTOISOMERIZABLE GUEST OR HOST COMPONENTS... 

Non-covalent bonds include ionic and dipolar interactions, hydrogen bonds, aromatic interactions (jt-jt, cation-jt and anion-7t), closed shell interactions and van der Waals interactions. Supermolecules generally comprise a host component with convergent binding sites and a guest component with divergent binding sites. 

Further research will probably develop in the direction of improving the control over particle size, size distribution, and particle positioning and preparation of freestanding films or well made monolith bulk samples with guest particles. So both guest and host components of such materials need to be optimized and further developed. 

D. Comolecular Aggregates of Urea/Thiourea and Other Host Components. 216... 

It is noted that the types of host lattices formed are dependent on the stoichiometric ratio of urea derivatives to anions and cocrystallized solvent molecules (water in most cases) or neutral molecules as additional host components. 

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